if you are looking at Hilton then make sure you get yourself Gold as soon as possible. There's a signup promo on now for Visa signature cards, but I think it might be USA only (look in the HH forum here for details), otherwise sign up for Hilton Racing to get Gold after 4 stays. The Hilton forum moan about Gold being worthless but in Europe I have only not managed an exec floor upgrade once in the last 70 or so stays (and that was the Stockholm Slussen the night before the Royal Wedding, with the hotel totally sold out).